The present invention relates to information recording and reproducing. More particularly, the present invention relates to a magnetic recording medium in magnetic recording, and it proposes a method of manufacturing a vertical magnetic recording medium, specifically, a method of manufacturing a granular medium. Further, the present invention relates to a constitution of the granular medium manufacturing method and the manufacturing method thereof.
Existent magnetic recording media of an in-plane recording system involves a problem of thermal stability and improvement of the thermal stability characteristics has also been demanded. The thermal stability is a phenomenon in which signals recorded to a magnetic recording medium are decayed after the lapse of a predetermined time and, finally, the recording signals are lowered to a medium noise level and recorded signals cannot be read out. This is a result of progress for the refinement of magnetic particles due to higher S/N ratio coping with increasing recording density in recent years.
In order to solve the problems described above, a vertical magnetic recording system has been studied instead of the in-plane recording. The vertical magnetic recording system has attracted attention as a system capable of maintaining a good thermal stability in a high recording density region and also capable of attaining a sufficient S/N ratio. A general vertical magnetic recording medium comprises a vertical magnetic recording layer including a vertically magnetized film for recording information signals, a soft magnetic under layer for enhancing the recording-reproducing efficiency of signals, and plural non-magnetic layers having various functions such as improvement of the crystallinity and control for the crystal grain size of the vertical recording layer.
In the film-forming technique for a vertical magnetic recording medium, particularly, a magnetic film, various studies have been made so far. In recent years, with the demand for the improvement of the recording density, vigorous improvement for the coercive force (Hc) has been made continuously in magnetic recording media, particularly, magnetic disks for use in HDD.
For the magnetic film composition used in the sputtering of magnetic films in order to develop the vertical magnetic anisotropy, some have proceeded to add B, Si, Ta, Ti, Zr, Al, W and oxides thereof as a fourth additive element to CoCrPt series media. Among them, the method of adding the oxides has been most frequently adopted in forming a granular magnetic film. For example, Patent Document 1 (JP-A No. 2002-342908) discloses using a target in which Cr2O3, TiO2, ZrO2 or Y2O3 is used in admixture together with a magnetic film containing an Si oxide mainly comprising CoCrPt on a substrate made of a resin. Further improvement of the magnetic characteristic provided by the addition of SiO2 and addition of O2 upon sputtering in addition to Ar is well-known.